Sri Mongkol (SMK) is providing passennger bus service going to east area of Thailand such as:
Nakhon Ratchasima
Buri Ram
Surin
Si Sa Ket
Ubon Ratchathani
Nang Rong
Prakhonchai
Prasat
Sangkha
Kantharalak
DetUdom
Their bus also goes to Kanchanaburi.
Their bus terminal in Pattaya is located at Third Road, close to intersection of Third Road and Pattaya Klan (Central) Road. The terminal is easy to reach from Pattaya central area, since you can walk from the intersection.